The contribution made by injection drug use to the HIV/AIDS pandemic in sub-Saharan Africa has received little scientific attention. The "TANZANIAN AIDS PREVENTION PROJECT, (TAPP)," will investigate injection drug use in Sub-Saharan African. TAPP builds on research we have been conducting for the past two years in Dar es Salaam, Tanzania. Our studies strongly suggest that injection drug use may be a significant contributor to the AIDS pandemic in Africa, especially in urban areas. TAPP has six specific aims. They are: to describe the environmental barriers to and facilitators of safer needle use and sexual practices; to describe the nuances of needle sharing and sexual practices within dyad structures; to describe the effect of social stigma as a barrier to acceptability of HTV testing and educational activities; to estimate HTV prevalence among drug injectors in Dar es Salaam; to estimate the prevalence of safe/unsafe needle use and safe/unsafe sexual behaviors within dyad structures; and to estimate safer needle use and condom use intentions within dyad structures. We will accomplish these aims using a mixed method research design composed of qualitative and quantitative components. Data collection will be guided by the Social Cognitive Theory. Data will be collected from purposeful samples of injection drug users residing in seven neighborhoods in Dar es Salaam. The two components of the mixed design are complementary, each producing data that, when triangulated, will provide a rich assessment of the HTV injection drug risk environment, prevalence of HTV among injection drug users, and sufficient social cognitive data to guide the development of interventions to decrease HTV incidence related to injection drug use that are relevant to the Tanzanian context.